let a: [string, number]
a = ['sss', 10]
// a[2] = 'crism'
console.log(a[1])

// 联合类型
let num: number | null = 3
num = null

// 类型强转
let anyValue: any = 'I am Crism.'
// let strLen: number = (<string>anyValue).length
let strLen: number = (anyValue as string).length
console.log('anyValue to String strLen: ',strLen)